Abstract [en]

The Molten Carbonate Fuel Cell (MCFC) is a high temperature fuel cell for stationary applications. It has the same high over-all efficiency (90%) as traditional combined heat and power plants, but MCFC can be built in small modules (from 250 kWe). The small modules in combination with fuel flexibility (natural gas, biogas, ethanol, diesel) makes MCFC an interesting alternative for industries with organic waste and high demands for reliability. The high temperature (650 °C) and the presence of molten salt result however in material degradation. Corrosion and dissolution of the materials used have been the challenge for MCFC. Although long-term field trials have shown that some of the material problems are not as severe as first believed, further material development is necessary to decrease the cost and prolong the life-time.

In the first part of this work, materials for different parts of the cell were tested within the EU project IRMATECH. The materials were interesting alternatives to the state-of-the-art materials due to their lower cost and/or better performance. Two alternative anode current collector materials were tested. For the anode current collector the corrosion and electrical resistance of the possible oxide layer are key parameters. These parameters were investigated and evaluated. Although both the materials showed a low resistance, there were indications of corrosion processes which could affect the life-time of the material.

For the cathode material, NiO, the dissolution of the material has been a problem. The dissolved nickel ions precipitate in the electrolyte and form conductive nickel dendrites that eventually short-circuit the cell. Therefore, the nickel dissolution of three alternative cathode materials was tested. The most promising material, a NiO doped with magnesium and iron, was tested in a single cell to study the electrical performance, the morphology after operation and the area where nickel had precipitated. The results showed that the performance was comparable to NiO, but it is necessary to investigate the mechanical strength of the material further.

In the wet-seal area, the stainless steel is coated with an aluminium coating to protect the material from a severe corrosion environment. The production of aluminium coatings has so far been expensive and complex and an alternative coating process was evaluated. The alternative coating, tested in both reducing and oxidising environments showed a tendency to crack and expose the stainless steel to the corrosive environment. This was suggested being due to the manual coating process that resulted in inhomogeneous coatings.

In the second part, an alternative process to coat the wet-seal was suggested, based on recently published results where aluminium had been electrodeposited from ionic liquids. These solvents have a wider electrochemical window than water, and electropositive materials can therefore be deposited. To make the coating process suitable for industrial applications, an alternative to the commonly used AlCl3 was tested. It was shown however, that the influence of the environment had to be investigated before any materials could be produced. The environment, especially water in combination with oxygen was shown to influence the cathodic current density. In absence of these components, the ionic liquid was shown to be very stable.

Capobianco, Paolo

Abstract [en]

Corrosion of metallic parts is one of the life-time limiting factors in the molten carbonate fuel cell. In the reducing environment at the anode side of the cell, the corrosion agent is water. As anode current collector, a widely used material is nickel clad on stainless steel since nickel is stable in anode environment, but a cheaper material is desired to reduce the cost of the fuel cell stack. When using the material as current collector one important factor is a low resistance of the oxide layer formed between the electrode and the current collector in order not to decrease the cell efficiency. In this study, some candidates for anode current collectors have been tested in single cell molten carbonate fuel cells and the resistance of the oxide layer has been measured. Afterwards, the current collector was analysed in scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). The results show that the resistances of the formed oxide layers give a small potential drop compared to that of the cathode current collector.

Scaccia, Silvera

Abstract [en]

The Molten Carbonate Fuel Cell (MCFC) converts chemical energy into electrical energy and heat. Since the working temperature is high, less expensive materials can be used compared to low temperature fuel cells. However, the components of the fuel cell still need to be improved. The dissolution of the NiO cathode has, for a long time, been a problem for the Molten Carbonate Fuel Cell (MCFC) and this area is still the focus for MCFC component research. In this study, solubility measurements for a NiC) cathode material doped with magnesium and iron are carried out and the electrochemical performance of this cathode material is tested under the standard conditions of the MCFC over 2,000 hours and compared with the performance of a standard NiO cathode. After operation, nickel precipitation in the matrices is investigated. It is concluded that a NiO cathode with magnesium and iron could be a viable candidate material for the MCFC.

Abstract [en]

Although water- and air-stable ionic liquids have been in use for some years, experiments found in the literature are still per-formed in inert gas with ppm levels of oxygen and water. In this study, the influence of different environments (vacuum, argon, nitrogen, air and oxygen and water) on the cathodic electrochemical window of the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) is reported and compared with investigations and processes found in the literature. The investigation indicates that this ionic liquid is highly stable in a vacuum and under argon flow. However, its cathodic stability is reduced in nitrogen and dry air. The simultaneous presence of water and air strongly affected the useful electrochemical window, as seen previously for imidazolium-based ionic liquids.

Abstract [en]

Although research in the field of ionic liquids for electrochemical applications has led to a deeper knowledge in their electrochemical properties, doubts in the interpretation of the experimental results are still encountered in the literature due to the poor control of the experimental conditions and/or to the limited number of experiments conducted. In this work, the effect of water and oxygen traces on the cathodic stability window of hydrophobic, air-stable ionic liquids composed of N-alkyl-N-methylpyrrolidinium (PYR1A') cations and bis(trifluoromethanesulfonyl)imide (TFSI-) anion, is reported. The extensive investigation performed by linear sweep voltarnmetry (LSV) and cyclic voltarnmetry (CV) indicates that the TFSl- anion is cathodically stable if the ionic liquid is pure and dry. The N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids investigated showed featureless cathodic linear sweep voltarnmetry curves before the massive cation decomposition took place at very low potentials.